In wireless mobile ad hoc communication networks, such as V2V communication networks, the problem of radio resource allocation (or scheduling) has to be addressed, i.e., how to schedule radio transmissions in a wireless mobile ad hoc communication network with minimal interference.
In order to determine whether a radio resource may be used for data transmission in a wireless communication network, the following multiple access constraints must be taken into account: (c1) a node cannot transmit and receive at the same time; (c2) the signal-to-interference-plus-noise ratio (SINR) at every receiver must be above a certain desired level. These multiple access constraints are explained in more detail on the basis of the exemplary wireless communication network 200 shown in FIG. 2, where node i may wish to transmit to node j (unicast). In FIG. 2, solid dots represent transmitting nodes, hollow dots represent receiving nodes, solid lines denote desired communication and dotted lines denote undesired interference.
If, in the exemplary wireless communication network 200 shown in FIG. 2, node i is allowed to transmit to node j while node i receives from node k, node i's transmission may cause sufficient interference at node l to degrade communication over link (k,l). On the other hand, if node i chooses a radio resource to transmit to node j in which node m transmits to node n, node m's transmission may cause sufficient interference at node j to degrade communication over link (i, j).
In accordance with constraints (c1) and (c2), a given radio resource s may be allocated for data transmission from node i to node j if and only if: (1) the constraints c1 and c2 are satisfied for node i, i.e., (1a) node i is not scheduled to transmit or receive in radio resource s, and (1b) the interference caused by node i's transmission can be handled by every node l receiving in radio resource s, and (2) the constraints c1 and c2 are satisfied for node j i.e., (2a) node j is not scheduled to transmit or receive in radio resource s, and (2b) the total interference from all nodes m transmitting in radio resource s can be handled by node
When a transmission from node i is intended for all its neighbors (i.e., a broadcast message), constraints 2a and 2b must be satisfied for every neighbor j of node i.
If nodes are mobile (as implied by the velocity vectors in FIG. 2), the interference constraints 1b and 2b must (ideally) be ensured for the entire duration of the radio resource allocation.
In an attempt to fulfil the interference constraints, many approaches, for instance, Young, C. D., “USAP Multiple Access: Dynamic Resource Allocation for Multiple Multichannel Wireless Networking”, Proc. of IEEE MILCOM 1999, 1:271-275, October 1999, require that no neighbor of node i be receiving and no neighbor of node j be transmitting in radio resource s. Such topology-based scheduling strategies have little overhead, but do not reflect the properties of wireless channels well. Moreover, these conventional approaches assume that all transmissions are omnidirectional, and are thus too conservative (i.e., spectrally inefficient), as they prevent significant radio resource reuse in networks where nodes may support beamforming.
Beamforming has the potential to dramatically increase radio resource reuse, and therefore network capacity, as a result of the much higher number of collision-free transmissions that may take place in parallel. If node i uses beamforming for transmission to node j, the energy radiated toward other neighbors l is minimal. Similarly, if node m uses beamforming for transmission to node n, the energy radiated toward node j is minimal. Thus, transmissions over all communication links (k,l), (i,j) and (m,n) may occur in the same radio resource without interference. A similar result is obtained when receive beamforming is used at node l and/or node j.
Supporting directional antennas in the design of radio resource scheduling algorithms has been addressed, for instance, in Bao L, Garcia-Luna-Aceves JJ, “Transmission Scheduling in Ad Hoc Networks with Directional Antennas”, Proc. of the 8th Annual International Conference on Mobile Computing and Networking (MobiCom), September 2002, which discloses a distributed receiver-oriented multiple access (ROMA) scheduling protocol for ad hoc networks with antennas capable of forming multiple beams. This approach incurs very little overhead. However, radio resource reuse is based on geometry (angular profiles), which does not take into account side lobes and may not work well in multipath channel environments, making it difficult to guarantee a given SINR target. Furthermore, this approach assumes that every node is equipped with a directional antenna. Thus, this approach cannot be applied to communication networks where some nodes use omnidirectional antennas.
Another approach was disclosed in U.S. Pat. Nos. 7,333,458 and 7,855,997 in the context of military communications. This approach, however, relies on the exchange of position information (e.g., GPS coordinates), which may not be available in certain situations, such as in a tunnel or urban canyon. Even when available, small inaccuracies in GPS location (±1 m) can lead to significant errors in the computation of direction if nodes are very close (within a few meters). Also, the approach disclosed in U.S. Pat. Nos. 7,333,458 and 7,855,997 is designed with a line-of-sight (LOS) channel in mind, which makes sense for aircraft-to-aircraft links. However, in future vehicular networks, for example, links may suffer from significant multipath fading, and a line of sight may not always exist between nearby nodes.
Grönkvist, J., “Interference-based Scheduling in Spatial Reuse TDMA”, Doctoral Thesis, Royal Institute of Technology (KTH), Stockholm, Sweden, 2005, discloses an approach based on interference-based scheduling. This approach is limited to omnidirectional antennas and incurs considerable overhead, as interference measurements are exchanged among neighbors.
Thus, there is a need for an improved wireless communication device and method for communication in a wireless communication network, in particular a V2V communication network.